On-Board Diagnostics (OBD) is a computer-based system built into more recent light-duty cars and trucks. OBD monitors the performance of some of the major components of a vehicle engine, including individual emission controls. The diagnostics system can provide vehicle owners or users with an early warning of malfunctions by way of a dashboard indicator, such as a “Check Engine” light (also known as a Malfunction Indicator Light (MIL)). By providing this warning, OBD allows the early identification of potential problems in the engine before the problems increase in severity. Modern OBD implementations provide realtime data in addition to recording appropriate codes from a standardized series of diagnostic trouble codes (DTCs), which allow a technician or other user to rapidly identify and remedy malfunctions in vehicle systems.
One of the more difficult diagnostics for engines is misfire detection. A misfire of an engine cylinder can be caused by a variety of sources, such as little or no fuel available (no injection), no atomization of the fuel (e.g., caused by the tip of an injector breaking off), loss of compression, incorrect timing of a spark plug for that cylinder, or other malfunctions. Automobiles can run a misfire diagnostic test to check for misfires. For example, many current Chrysler products have an active misfire algorithm This algorithm slowly over-fuels one injector at a time and looks for an equivalent engine speed increase. This algorithm is viable in these products because of the limited vehicle configurations that are used, e.g., one manual transmission configuration and one automatic transmission configuration are produced. This requires only a very small number of different calibrations to be needed for the algorithm for each different configuration.
However, such active misfire algorithms (speed-based misfire detection methods) are not appropriate for more specialized vehicles and engines, for example those used in heavy duty applications. This is due to the variation in configurations and applications, including different driveline inertias, transmission types, accessory loads, etc. Speed-based methods can be very complex due to the wide variety of driveline configurations and accessory loads, and such methods can require unique calibrations for each application (different combinations of transmission, driveline, and accessory loads). All of the different variations needed for different applications and configurations would require individual calibrations if the active misfire algorithm were used.
Knock sensors (accelerometers) are used on passenger cars for detection and control of engine knocking. However, detecting misfires using only knock sensors is not a viable alternative, since variations in engine mounting can cause changes in signal quality and significant calibration effort would be required to tune an algorithm to robustly detect misfires at all engine conditions. In addition, besides engine mounting issues, other characteristics can add noise to calibration and vibration detection, including driveline dynamics and accessory loads on the engine (e.g., a hydraulic pump, water pump, etc.).
Accordingly, a system and method that can diagnose engine misfires robustly and that can accommodate a wide variety of different configurations and applications in vehicle and engines without extensive calibrations would be desirable in many applications,